Fiberglass reinforced materials, such as fiberglass reinforced plastic, fiber-reinforced plastic, and fiber-reinforced polymer, have long been used in a number of commercial and consumer applications. Among other attributes, fiberglass reinforced materials have a high strength to weight ratio, are relatively inexpensive, non-conductive, and non-corrosive. As such, components made from fiberglass reinforced materials are commonly found in vehicles, such as automobiles, boats and planes; pipes formed from fiberglass reinforced materials are used in many industrial processes; and fiberglass reinforced materials are used in structural applications, where it is commonly used to strengthen concrete and steel beams.
One common use for fiberglass reinforced materials is in the manufacture of ladders and other climbing products. Ladders are generally manufactured from wood, aluminum, fiberglass reinforced materials, or a combination thereof. The choice of ladder material depends on the intended use, the weight of the ladder, and cost. For example, wood ladders have significant variations in quality and are more susceptible to moisture and the elements as compared to aluminum and fiberglass ladders. Ladders constructed of aluminum are strong, durable, and lightweight, but conduct electricity. Ladders constructed from fiberglass reinforced materials, in addition to being strong and durable, are non-conductive. Prior art fiberglass reinforced ladders, however, are heavier than equivalent aluminum ladders (i.e., those having the same shape, size, and rating).
Because aluminum conducts electricity, aluminum ladders cannot be used near power lines or electrical wiring. As such, non-conductive fiberglass reinforced ladders are commonly used in these situations. However, traditional fiberglass reinforced ladders typically weigh 15% to 20% more than an equivalent aluminum ladder. This additional weight is undesirable and is a burden to the individuals transporting and using the ladder. For example, power company, cable company, and telephone company workers must load and unload the heavier fiberglass reinforced ladder for each installation or work assignment. In some cases, the heavier weight of the fiberglass reinforced ladder can contribute to fatigue or injuries.
Fiberglass reinforced ladders are traditionally manufactured by a pultrusion process. Prior art pultrusion processes involves impregnating reinforcing material with a resin, forming the resin coated reinforcing material into the desired shape with a die and curing the resin by the addition of heat.
Techniques have been developed to reduce the weight of fiberglass reinforced ladders made by prior art pultrusion processes. One such technique involves cutting a series of holes at regular locations along the length of the ladder rails. These holes are in addition to the holes formed for the purpose of mounting the rails. The reduction of material results in a reduction in the overall weight of the ladder. Companies, however, often label the ladder rails with the company name, a trademark, logo, or other content. The holes, while reducing weight, inhibit such labeling. The holes also introduce other problems, such as (i) reducing the structural integrity of the ladder, which can, over time, lead to a failure under load resulting in bodily injury or property damage, (ii) increasing cost as a result of the additional step in the manufacturing process to produce the holes, and (iii) increasing the complexity in the manufacturing process to properly align the holes so the rungs can be attached.
Accordingly, it would be an advance in the state of the art to develop a process to make a lightweight fiberglass reinforced ladder that can be made using traditional pultrusion manufacturing equipment and that has a weight near, or less than, that of an equivalent aluminum ladder, while retaining the shape, appearance and structural integrity of a fiberglass reinforced ladder made using traditional processes.